The present invention is directed to an explosive powder charge operated setting tool having a support member including a cartridge chamber at one end with a piston guide axially displaceable within the support member, and a driving piston located in the piston guide and having a cylindrical shank extending axially in the driving direction from a head. The driving piston is driven by propelling gases generated from an explosive powder charge contained in the cartridge chamber and is axially displaced from a trailing initial position into a leading driven position. A retention device for the driving piston includes at least one radially displaceable ball bearing against a conically shaped inside surface of an annular spring washer. The ball is displaceable to a limited extent parallel to the axial direction of the piston guide in a holding part open towards the shank of the driving piston.
An explosive powder charged operated setting tool is disclosed in DE 43 13 504 A1 containing a supporting member with a cartridge chamber, a piston guide positioned within and displaceable relative to the support member, a driving piston mounted in a guide bore in the piston guide, and a retaining arrangement. The driving piston is displaceable through a volume, formed by the guide bore in the piston guide and by a portion of the support member, by propelling gases generated by an explosive powder charge ignited in the cartridge chamber. The driving piston is formed of a cylindrical shank with a head at one end. The retaining arrangement is formed by a receptacle in the piston guide open in the radial direction towards the cylindrical shank of the driving piston, with two balls resting on the shank and an annular spring washer enclosing the balls. The length of the receptacle parallel to the length of the driving piston is greater than the diameter of the balls. The annular spring washer has a conically shaped inside surface in contact with the balls and inclined relative to the axis of the driving piston and forming an angle sloping outwardly in the direction opposite to the driving direction of the piston.
If the driving piston moves slightly in the driving direction, the balls roll in the driving direction. The balls rolling on the conically shaped inside surface of the annular spring washer press against the washer radially outward and also are pressed by the flexural force of the spring washer radially inward against the shank of the driving piston, so that an automatic displacement of the driving piston in the setting direction especially due to gravity is prevented. During the driving operation, the driving piston is accelerated in the setting direction by the very high energy developed by the explosive powder charge. In comparison, the retaining force acting on the shank by the retaining arrangement is negligibly small, so that the retaining force does not have a harmful effect on the acceleration of the driving piston.
In particular, if the driving piston is accelerated by excessive energy, the piston strikes, after driving a fastening element, at a high velocity against a surface of the support member in the region of the cartridge chamber facing in the setting direction and then rebounds moving again in the driving direction, so that it does not return into its initial position. During a subsequent driving operation, the driving piston cannot be sufficiently accelerated, whereby the fastening element cannot be driven into the receiving material for a sufficient depth.